Category Archives: Plants

Plants of the Chihuahuan Desert region.

Places: Big Bend Ranch State Park’s Arroyo Mexicano

Big Bend Ranch State Park covers 311,000 acres of the Chihuahuan Desert.

Big Bend Ranch State Park: The Other Side of Nowhere

Big Bend Ranch State Park hugs the Mexican border and sprawls over 311,000 acres of the Chihuahuan Desert in West Texas. State park staff affectionately call it “The Other Side of Nowhere.” To the casual visitor, the park appears to be all rugged mountains, deep canyons, and miles and miles of rough roads designed to destroy your vehicle and shake the fillings loose from your teeth.

But those rugged mountains and deep canyons hold treasures if you’re a naturalist. The rough roads? They’re just a necessary evil if you want to experience the park.

Groves of cottonwood and ash trees line the bottom of Charro Canyon.

Cottonwood, Ash, and Oak Trees Line the Bottom of Chorro Canyon

I spend two days with Blaine Hall and Roy Morey exploring sites for a Native Plant Society of Texas field trip. Blaine aka “Big Foot” wears one shoe 3 sizes larger than normal to accommodate the brace and bandages that stabilize an ankle broken during a hike two weeks ago. Recently retired from his position as the interpretive ranger for Big Bend Ranch State Park, Blaine chatters away, teasing Roy and me, and pointing out geologic features as he skillfully guides the truck up rock-covered slopes, across ridges of limestone, and down sandy washes. He pulls over frequently so that we can enjoy the view.

Roy is quiet, not letting Blaine’s teasing phase him. Roy is a plant person. After retirement, he moved to Terlingua and began compiling photographs of the plants of Big Bend National Park. His hobby became a full-time pursuit, ultimately resulting in Little Big Bend: Common, Uncommon, and Rare Plants of Big Bend National Park. Once he completed that book, Roy shifted west and began working on a companion volume that will describe the plants of Big Bend Ranch State Park.

“I need to get up there someday,” says Roy, looking up at the sheer cliffs of a mountain. I’m surprised. Between Roy and Blaine, I would have sworn that they’ve walked every inch of the park’s 311,000 acres.

Today, we’re looking for unusual plants, so we head for Arroyo Mexicano, a box canyon that ends at Mexicano Falls. Canyons often harbor botanical treasures such as groves of cottonwood and ash trees and tiny plants that cling to the rock walls. Canyon walls protect plants from the harsh sun and fierce winds of the desert and often have seeps and springs that provide extra moisture. “One of the only mountain laurels in the park is up Arroyo Mexicano,” says Roy. “I hope it’s still alive.” It was.

An ammonite impression in limestone.

A Dinner-Plate Sized Ammonite Fossil in the Limestone

“Want to see an ammonite?” Blaine asks as we drive down Fresno Canyon. The creek has eroded deeply into the rock, exposing the flat-lying, flaggy Cretaceous limestone of the Boquillas Formation and the nobby, white limestone of the Buda Formation.

We pile out of the truck to admire the dinner plate-sized ammonite lying exposed on an upturned piece of Boquillas limestone. The thick limestones and this ammonite fossil are evidence of a time when a shallow sea covered part of Texas. You won’t see ammonites swimming around today. The last of them went extinct when a giant meteorite struck the earth about 66 million years ago. The short and long-term effects of the meteorite impact—wildfires, tsunamis, and clouds of debris that blackened the skies and blocked the sun for years—killed about ¾ of Earth’s plants and animals.

A Mexican Buckeye Provides Nectar for Pollinators

Mexican Buckeye Tree on the Edge of the Arroyo

We eventually arrive at the mouth of Arroyo Mexicano, shoulder our packs, and trudge our way up the canyon. I’d like to say that we hiked briskly, but I have to admit that I’m a trudger in soft sand. Fairly quickly, we see pools of water and a shallow stream meandering its way across the sand bottom. Groves of cottonwoods, their new leaves a beautiful, fresh spring green, provide shade along the way.

Occasionally a spot of pink reveals the location of a Mexican buckeye tree. These early-blooming shrubby trees are an important source of nectar for bees and butterflies. A Mournful Duskywing flits between flowers, ignored by a nectaring Grey Hairstreak. I search unsuccessfully for a Henry’s Elfin—a small brown and silver butterfly that uses Mexican buckeyes as a host plant. Henry’s Elfins are more common in the eastern United States, so seeing one in West Texas is pretty special. Roy and Blaine have moved on, so I quit looking for butterflies and hurry to catch up.

Huge velvet ash trees with their gnarly roots exposed.

Velvet Ash Trees in the Arroyo

As we move up the canyon, we walk under large velvet ash (Fraxinus velutina) trees. I am fascinated by the texture of the bark and the thick, gnarly roots wrapped around giant boulders. Of course, the exposed roots are also a warning sign. This canyon carries water—often with enough force to roll boulders and wash away enough sediment to expose the roots of trees. I check out the sky (gray clouds gathering) and look for high ground. The vertical walls of the canyon look back. I’m doomed.

Conglomerate boulder made of smaller, rounded, igneous rocks.

Volkswagen-sized Conglomerate Boulder in the Arroyo

In places, we skirt boulders the size of Volkswagon Beetles or larger. I envy Blaine his ability to read these rocks. “See,” he says, “this rock is made up of older rocks that have been cemented together to form a conglomerate.” This particular conglomerate is just a baby rock if you can wrap your mind around geologic time.

All of the “clasts” or smaller rocks that make up the conglomerate are volcanic in origin which means they were deposited about 27 million years ago. Over time, they broke away from their parent rock, were tumbled and smoothed, and came to rest in one place long enough for the white matrix rock to cement them all together again. The conglomerate eventually broke up, and Volkswagon-sized boulders tumbled down the slope, coming to rest in the stream bed.

Fern-covered walls and plunge pool of Mexicano Falls

Mexicano Falls at the End of the Arroyo

After about 3.5 hours of walking and stopping to admire rocks, plants, and scenic views we reach the end of the canyon. At this time of year, Mexicano Falls is more of a drip than a fall. Maidenhair ferns, yellow-flowered columbines, and thick carpets of moss fill the cracks where water seeps from the rocks. The plunge pool is thick with green algae.

Blaine points to a gap in the canyon rim where water funnels through to create a waterfall during the summer rainy season. I’d love to be there to see the waterfall, but then I remember those exposed roots and the flood debris wrapped three to four feet high up the trunks of the trees that we were walking through earlier. Flash floods are real and dangerous in this canyon.

The tiny, yellow, fringed monkeyflower hangs from the wet walls of the canyon.

Fringed Monkeyflower Hangs from the Wet Walls of the Canyon

While Blaine and I photograph the ferns and columbines, Roy walks the face, scouring the seeps for fringed monkeyflower (Mimulus dentilobus). “Found it!” he calls. Fringed monkeyflower is a rare plant in Texas, found only in places where water drips from the West Texas mountains. I’m surprised by how tiny it is. The bright yellow flower with its fringed petals and red spots in its throat rises above a mat of small leaves hugging the wet rock face. We’re lucky to find these in bloom. It’s only March and according to the field guides, fringed monkeyflower blooms from June to August.

Blaine and Roy fix a flat tire.

Flat Tire

The wind begins to blow, and the clouds build, getting thicker and grayer. We decide to return to the truck before a storm drenches us. The hike back takes about 2.5 hours. We quickly pack up and drive off, but Blaine stops almost immediately. He walks around the truck and discovers a flat tire. “That’s two this week,” he mutters. Razor-sharp rocks can slice through the sidewalls of a tire and mesquite thorns pierce treads easily. We unload all the gear to access the spare, and Blaine and Roy begin the laborious task of changing the tire. Fortunately, nothing goes wrong and within 30 minutes we’re back on the road. We eliminate a couple of side trips and head straight back to the park headquarters at Sauceda. Driving any further than necessary without a spare is foolish.

The flatirons of the Solitario provide a perfect backdrop for a patch of Big Bend Bluebonnets.

Big Bend Bluebonnets and the Solitario

Since Blaine and Roy have the flat-tire situation in control (and they’re a bit annoyed with my photographic documentation of the event), I wander off a few feet to photograph a patch of Big Bend bluebonnets with the flatirons of the Solitario in the background. The Solitario is a massive igneous dome created when molten rock pushed up the flat-lying rocks above it creating a circular feature 10 miles in diameter. The dome attracts geologists, botanists, and naturalists from around the world and is probably the most famous feature in Big Bend Ranch State Park.

I love going to the Solitario, but this opportunity to explore Arroyo Mexicano with Blaine and Roy was as close to perfect as a day could be.

Also posted in Chihuahuan Desert, Geology, Texas Tagged , , , |

Monarch Conservation in West Texas

Monarchs roost in a pecan tree in Alpine, Texas

The sun is setting as I sit on the picnic table and just watch. Monarchs swirl around me by the hundreds—or is it thousands? They begin to settle, landing in rows on the bare branches of the old pecan tree near Kokernot Lodge in Alpine. They’re restless though, and burst into flight again when a newcomer tries to squeeze into the row. A swirl or two and they resettle on a clump of leaves. More butterflies float in from the north and jostle for space. I am amazed by the utter silence. A butterfly wing doesn’t even whisper.

Monarch Migration
Monarchs are one of the few insects that migrate in great round-trip journeys from their summer breeding grounds in the north, to sites in the south where they overwinter. In the spring, they head north again. The earliest report of monarchs migrating south was published in a Canadian journal in 1857. The author, W.S.M. D’Urban, noted that monarchs appeared in the Mississippi Valley “in such vast numbers as to darken the air by the clouds of them.” But it took another 120 years to discover where they were going.

In the late summer, as the nights grow cooler and the days grow shorter, a generation of monarchs emerges from their chrysalides that are biologically and behaviorally different from the generation before them. These monarchs won’t mate or lay eggs until the following spring. Their driving instincts are to find food and fly south.

They travel in pulses, often driven by cold fronts that bring the wind from the north, sometimes traveling 150 miles in a single day. Late in the afternoon, the butterflies seek a place to spend the night—in Texas, this is usually a pecan or oak tree near water. Although monarchs do not migrate in flocks as birds do, individual monarchs seem to seek each other out to form roosts of hundreds to thousands of butterflies. The next day, warmed by the morning sun, they will continue their journey south.

When the winds are unfavorable, monarchs stay on the ground, nectaring on goldenrods, gayfeather, and mistflowers. These nectaring stops allow the monarchs to build up fat reserves that will sustain them throughout the winter.

By late September, all of the monarchs from the 5.2-million-square-mile breeding grounds east of the Rocky Mountains funnel into Texas. Most years, the monarchs will travel through Texas along the central flyway, a broad swath of land 300 miles wide and centered on a line between Wichita Falls and Eagle Pass. They are headed for the fir forests of the Transverse Neovolcanic Belt near Mexico City, a place that none have been before, but that millions will find.

Monarch Conservation
D’Urban’s skies darkened by clouds of monarchs are pretty much gone. In fact, some predict that the great monarch migration may be a biological phenomenon that winks out in our lifetime. Illegal logging of forests in Mexico, changing climate in both the overwintering grounds and the summer breeding grounds, and the decrease in nectar and larval host plants are all taking their toll.

A world without monarchs scares people, so many organizations and agencies are jumping on the monarch conservation bandwagon. Yesterday, Texas Parks and Wildlife Department released the Texas Monarch and Native Pollinator Conservation Plan (October, 2015) or perhaps better titled The I-35 Monarch Conservation Plan. Don’t get me wrong. I’m proud of TPWD and the many partners listed in the report for recognizing the critical role that Texas plays in monarch conservation and for wanting to do something about it. But—ahem—that beautiful flyway map produced by Monarch Watch? It’s just an average. Monarchs scoff at sharp lines on human-drawn maps. This year, thousands are monarchs are passing through Fort Davis, Alpine, Marathon, and Terlingua on their way to Mexico. As they have in the past and they will in the future.

Fall Migration 2015

Journey North map of the 2015 Fall Monarch Migration

 

This particular pet peeve of mine is not new. About 10 years ago, I read an article about a monarch tagging project being conducted by the Southwest Monarch Study of Arizona. They were finding that many of their monarchs chose to overwinter in sunny California rather than Mexico. This got me thinking about the Trans-Pecos monarchs. Where were they going?

I eagerly contacted the Southwest Monarch Study and asked to be part of their tagging program. “You’re too far east,” they told me. “Contact Monarch Watch.” Monarch Watch told me to contact Texas Parks and Wildlife and Texas Parks and Wildlife told me we were too far west for our monarchs to be of any interest.

I gave up, but the monarchs haven’t. In fact, the frequency of the monarch migration through west Texas seems to be increasing. Don’t quote me on this. It’s just a hunch without any supporting data. But it is an interesting research question. How does the monarch migration fluctuate over time and what are the triggers that cause a shift of the central flyway? What does long-term climate research predict for our region? Will El Nino patterns increase in frequency, resulting in wetter Fall weather and increased nectar sources for monarchs?

Conservation plans need to be pro-active and prepare for a changing future. I know that it’s easiest to focus on what we see today and concentrate on urban areas because funding is often about numbers (how many school children can you reach per dollar spent?), but if you’re truly interested in monarch conservation, think broadly and include west Texas in your planning.

In the meantime….
As I climb off my soapbox (will someone please hold the ladder?), I have some suggestions:

1) Plant for fall migration. You’ll read a lot about the need to plant milkweeds for monarchs. Milkweeds are important, it’s true, but in the fall, monarchs need nectar sources. A 2006 study of lipids (energy storage molecules) in migratory monarch butterflies showed that once monarchs get to Texas, they pause to nectar and build up their lipid reserves before continuing on to their final destination in Mexico. These lipid reserves are critical to their survival over the winter. Texas wildflowers are critical to their survival over the winter.

2) Go to the Big Bend Chapter of the Native Plant Society of Texas Facebook page and post an image of plants that you’ve seen monarchs use for nectaring. Let’s develop a list specific to this area for homeowners, landowners, and government officials that can be used for everything from large-scale restoration projects to home gardens.

GoldeneyeGregg's MistflowerAnnual Goldeneye
Texas GayfeatherMilkweedThistle
Fall blooming flowers such as sunflowers, mistflower, Annual Goldeneye, Gayfeather, milkweeds, and thistles provide important nectar sources for migrating monarchs.

 

3) While we would all like to think that our backyard gardens are Making A Difference, here’s what the 2006 monarch study has to say: “The popularity of butterfly gardens and native plant landscaping may enhance pollinator populations locally, but will never be of sufficient magnitude to compensate for the losses of native nectar sources from rural habitats.” Damn.

This isn’t to say that you shouldn’t be planting your monarch café. Please do. But also think bigger. Did you know that there are over 4 million miles of roadsides in the United States? I don’t know how many in Texas, but I’ve driven over 1,000 of these miles within the last week, so I can tell you that there’s a bunch. Thousands of miles of roadsides fenced off from grazing animals and protected from development.

The Texas Department of Transportation is responsible for managing these roadsides. They even have a wonderful document titled Roadside Vegetation Management Manual: Guidelines for Levels of Vegetation Management. Take a look at it. It’s great.

Unfortunately, when I called TXDOT one year to register a complaint about the mowing of a huge stand of gayfeather in full bloom, I was told the guidelines are “suggestions, not policy.” I think Texans and Texas deserve better than that. Make yourself familiar with the guidelines and work with your local TXDOT office to let them know that you care.

3) Post observations to Journey North. The only way they’ll know about the monarchs of west Texas is if we tell them.

Also posted in Chihuahuan Desert, Insects

Just Add Water: Annual Wildflowers in the Chihuahuan Desert

Prairie evening primroses dot a pasture near Fort Davis, Texas.

My friend, John Karges, and I were talking yesterday about the amazing spring that we’re having. He laughed and said “Add water and the desert will stir itself.”

How true.

We’ve had an extraordinarily wet winter and spring this year. Deep, soaking rains and frequent snow (and ice) storms encouraged a wildflower display that few can remember ever seeing in the Chihuahuan Desert region. Big Bend bluebonnets create a blue haze on the hillsides; the delicate, white petals of prairie evening primrose look like a tissue-box explosion in pastures; and mustard plants emit a perfume so sweet it’s cloying at times.

Big Bend Bluebonnets along the River Road in Presidio County Texas.

Even the stems of the cacti are so swollen with water they look like they’re going to burst. Instead, they’ve burst with flowers, dozens of blossoms covering a single plant.

The desert is in bloom. It’s a marvelous sight to behold.

Mustard wildflowers carpet a pasture in the Chihuahuan Desert near Marathon, Texas.

But where do all these flowers come from?

Most of the time, the Chihuahuan Desert is a pretty harsh environment. It’s dry (especially in the winter) and the rain that we do receive tends to come in the summer during highly localized thunderstorms that may drench one spot but leave a broad area dry as a bone.

To cope with the heat and the unpredictable precipitation patterns, desert plants have an amazing array of adaptations aimed at holding on to moisture: small leaves, fine hairs that protect the leaf surface, and a splendidly specialized photosynthetic process.

But during years like this one, we’re reminded of the most amazing adaptation of all: being an humble annual.

Annual plants are those that go from seed to seed in a very short time. When conditions aren’t favorable, the seed just doesn’t sprout. It sits in the soil, waiting for the perfect combination of moisture and warmth that will increase its chances of survival.

Dense patches of the annual wildflower curvepod scrambled eggs were common at higher elevations in the Chihuahuan Desert.

This life cycle isn’t unusual—in fact, approximately 13% of the world’s flora consists of annuals. But if you look at the flora of a typical desert, you’ll find something very different. In the aridlands of the world, annuals can make up 40% or more of the desert flora. Think about it. Nearly half of the plants growing in a desert won’t even make an appearance until there’s some hope of surviving long enough to be pollinated and set seed.

The seed of many desert annuals can survive for years—decades even—before the conditions are perfect for growth. On occasion, they get fooled, though. A good soaking rain followed by heat, wind, and dry conditions may spell doom for an overeager annual.  Long-term survival depends on mechanisms that discourage a portion of seed from growing even when conditions are just right.

But sometimes, spring conditions are just too favorable for any plant to remain snug in its seed jacket. This is one of those years. Good rains and warm day-time temperatures have encouraged the growth of hundreds of thousands of annuals. Early in the spring, clay flats in the Big Bend region were covered with turtleback—its gray-green leaves and cream-colored flowers forming a soft carpet across the landscape. Stands of lyreleaf twistflower (you’ve just got to love the name) sent their spikes of purple, urn-shaped flowers above the grasses, and curvepod scrambled eggs had even the plant enthusiasts scratching their heads. Where did they all come from?


Naked turtleback creates a green haze in the Chihuahuan Desert of Big Bend National Park, Texas.

 

Naked turtleback in the clay flats of Big Bend National Park, Texas.

The desert is truly spectacular this year and every week it changes. We’re still getting rain, so the show will go on. If you’ve been putting off your annual pilgrimage to the Chihuahuan Desert, it’s time to quit procrastinating, pack your camping gear, and come on out. This truly may be a once in a lifetime experience.

Also posted in Chihuahuan Desert, Landscapes Tagged , , , |

Chihuahuan Desert Ferns

Cheilanthes fern, Fort Davis National Historic Site, TexasNormally, I’m outside every day in September enjoying the cooler temperatures, brilliant sunshine, and abundant life inspired by the afternoon thunderstorms of the monsoon season.

But not last week.

Rain (torrential at times), heavy cloud cover, and temperatures in the low 50s kept me huddled in the house muttering about the imminent arrival of the next Ice Age. As I stared morosely out the window, watching the rain drip from the roof, I began to wonder: What happens to the butterflies, bees, and bugs when the temperatures go from warm and dry to cool and wet in a single day?

Thinking this was the perfect subject for a blog (I’m sure you’ve all been dying to know), I donned my rain jacket, grabbed my camera gear, and wandered through the mist to the Fort Davis National Historic Site. Although chiefly known for the 19th century fort buildings, they also have a wonderful nature trail that loops from the fort site, up the ridge that separates the Fort from Davis Mountains State Park, and back down again. Here, I was sure I would find my sleeping bugs.

I probably would have, too, if I hadn’t gotten distracted. Every place I peered and poked for insects, I was confronted by ferns. Beautiful, lush, green ferns. The magic of desert rain.

Dancing Bommeria, a Chihuahuan Desert fern, growing near Fort Davis, Texas.Most people don’t hot-foot it to the desert to look for ferns. But perhaps they should. According to botanists Sharon Yarborough and Mike Powell, there are 64 different types of ferns that grow in the Trans-Pecos region of Texas.

Ferns can grow in the desert because they’re experts at finding little microhabitats that are just a tinier bit wetter than the surrounding landscape. Look for them growing from cracks in the rock, under the shelter of a tree, or peeking out from beneath a boulder. Depending on when you look, though, you may not be overly impressed. In fact, during most of the year, desert ferns are brown, crispy, and look—well—dead.

Chihuahuan Desert ferns dehydrate during the warm, dry months and wait for rain.But fear not! Playing dead is just one of the many adaptations that ferns have for surviving in the desert. And what an adaptation it is. Your average plant can drop to about 75% moisture content before it begins to wilt and beg for water.  Creosote, one of our common desert shrubs, can lose about half its moisture before it begins to look a bit peaked.

But the ferns. Oh, the ferns. They are the masters of dehydration. During the dry season, some species can desiccate to less than 6%—or as dry as many seeds—but begin to green up, unfurl, and grow within an hour after a refreshing rainfall. When it dries up again, so do the ferns.

But ferns don’t give up their moisture easily. They may be able to survive as a brittle frond, but life is better when you’re green and photosynthesizing. So to stay green as long as possible, the ferns (and many other desert plants) have ways to reduce moisture loss.

Small Leaves

Small Leaves

Waxy Coating

Waxy Coating

Protective Hairs

Protective Hairs

Thickened Leaf Margins

Thickened Leaf Margins

Small is better. Most desert ferns are much smaller then their rainforest cousins. Remember that during the process of photosynthesis the plant takes in carbon dioxide and releases oxygen and water as a waste product. The smaller the leaf, the less water is released.

Be waxy. Most water is lost (transpired) from special cells on the leaf called stomata. These open and close to absorb and release gases (carbon dioxide, oxygen, and water). But other parts of the leaf surface and stem can lose water through simple evaporation. To help protect from this “incidental” water loss, many of the ferns have a cuticle of waxy deposits on the leave surface that make them thicker and seal in the water.

Get hairy. Have you noticed how many ferns are grey and fuzzy? If you look closely, you’ll notice that the color is due to a dense coating of hair. These light-colored hairs serve a couple of purposes. First they reflect light making the leaf surface temperature cooler and they efficiently trap rain, dew, and other forms of moisture to raise the humidity around the leaf surface. Keeping the air surface immediately around the leaf cooler and more humid reduces the evaporative demand from the atmosphere.

Thick leaf margins. The last defense against moisture loss is the ability of the leaflets to roll, thus protecting the surface and the spores. Many fern leaflets have thickened margins that enhance the ability of the leaf to roll.

Not all ferns found in the desert have these adaptations for dry conditions, though. Others simply seek places where there is enough moisture. Delicate maidenhair ferns, for example, can be found on many shaded rock faces with perennial seep springs. You can find these beautiful ferns at the bottom of Modesta Canyon at the Chihuahuan Desert Nature Center or in the grotto at Ojito Adentro, Big Bend Ranch State Park.

Water Clover (Marsileaceae) is a Chihuahuan Desert fern that grows in puddles during the rainy season.But my favorite fern is the water clover. This aquatic fern survives the dry season as a packet of spores (sporocarp) in the mud of ephemeral pools. When the rainy season arrives and the pools fill with water, the gelatinous interior of the sporocarp swells, rises to the water surface and splits, releasing the male and female spores. Once they do what males and females do, the newly fertilized embryo sinks to the bottom of the pool, takes root and begins to grow, eventually spreading its four leaflets across the surface of the pool to begin the cycle of life again.

It’s starting to rain. Time to go look for ferns!

Also posted in Chihuahuan Desert Tagged , , , , |

Dodder Discourse

Dodder

On a recent trip to Big Bend Ranch State Park, I was amazed by the amount of dodder growing by the side of the road. Tangled, yellow filaments—looking like a Silly String party gone wild—weighed down the branches of the shrubs.

Dodder is a stem parasite with a fascinating life history. It’s a plant that can see, smell, and even sweet-talk its host.

Dodder is typically an annual that starts life a little late, giving its unsuspecting host a head start. Once emerged, the seedling immediately begins to move, sweeping the area in a counterclockwise direction, looking for the perfect host. It can’t be just any plant. It has to be the right plant.

Dodders use phytochromes (pigments that plants use to detect light) and volatile cues to “see” and “smell” the plants around them. They avoid potential hosts that are too young or too sick leading one researcher to describe the search for a host as an “intelligent choice and intention.”

The dodder seedling must work quickly—its root organ will wither away within a few days leaving the dodder reliant on its host plant for almost all of its nutrients.

Once the dodder finds the perfect host (“welcome, come on in”), it wraps itself up the stem, producing haustoria that invade the host-plant cells. The hyphae or filaments of the haustoria hijack the host’s nutrient transport system, transferring food back to the dodder.

The host plant isn’t entirely passive during this process. They can, and often do, fight back with barrier tissues that block the dodder’s advancing hyphae or inhibitors that retard hyphae growth.

Research published in Science this week shows that dodder and its host plant “talk” to each through the exchange of messenger RNA molecules. So what are the plants talking about? Researchers aren’t in on the conversation yet, but one suggestion is that the dodder is engaged in some “sweet talk,” sending messages that instruct the host plant to lower its defenses and allow the dodder in.

A few species of dodder (who really are serious agricultural pests) have given the whole group a bad reputation. But Dr. Mihai Costea, a botanist at the Wilfrid Laurier University in Canada, says we shouldn’t be so quick to dismiss dodder.

According to Dr. Costea, dodder should be respected as a keystone species in some ecosystems.  Many host plants can be bullies. They grow fast and aggressively, crowding out the shy, retiring types. But dodder, through its ability to reduce the host plant’s biomass and alter the way it uses resources, can actually modify the structure of the plant community, keeping the bullies in check and allowing other plants to flourish.

I’m not sure which species of dodder I saw the other day (there are six that grow in the Trans-Pecos region of Texas), but I sure am glad I stopped to take a look at this fascinating little plant.

Sources

Costea, M. 2007 through present. Digital Atlas of Cuscuta (Convolulaceae). Wilfrid Laurier University Herbarium, Ontario, Canada.

Costea, M., and F.J. Tardif. 2006. The biology of Canadian weeds. 133. Cuscuta campestris Yuncker, C. gronovii Willd. ex Schult., C. umbrosa Beyr. Ex Hook., C. epithymum (L.) L. and C. epilinum Weihe. Canadian Journal of Plant Science 86:293-316.

Gunjune, K., M.L. LeBlanc, E.K. Wafula, C.W. dePamphilis, and J.H. Westwood. 2014. Genomic-scale exchange of mRNA between a parasitic plant and its hosts. Science 15 August 2014:345 (6198): 808-811.

Virginia Tech. 2014. Plants may use newly discovered molecular language to communicate. ScienceDaily 14 August 2014. www.sciencedaily.com/releases/2014/08/140814191939.htm.

Also posted in Chihuahuan Desert Tagged , , |